U.S. patent application number 10/662448 was filed with the patent office on 2004-04-01 for prismatic battery.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Kasahara, Hideki, Nakamaru, Hisao.
Application Number | 20040061476 10/662448 |
Document ID | / |
Family ID | 32024885 |
Filed Date | 2004-04-01 |
United States Patent
Application |
20040061476 |
Kind Code |
A1 |
Nakamaru, Hisao ; et
al. |
April 1, 2004 |
Prismatic battery
Abstract
A prismatic battery with tabless current collectors. Electrode
plates are wound to have a rectangular or elliptic cross section,
and current collectors formed of metal plates having a shape
conforming to this cross section are welded to the end faces of the
belt-shaped current collecting portions of the electrode assembly.
The metal plate includes a pair of lengthwise notches and a pair of
widthwise notches respectively extending from the center to the
periphery, and the opposing side edges of these notches protrude
orthogonally from the metal plate to form connection pieces, which
are welded to the belt-shaped current collecting portions of the
electrode assembly.
Inventors: |
Nakamaru, Hisao;
(Kamakura-shi, JP) ; Kasahara, Hideki; (Naka-gun,
JP) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1950 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
Osaka
JP
|
Family ID: |
32024885 |
Appl. No.: |
10/662448 |
Filed: |
September 16, 2003 |
Current U.S.
Class: |
320/107 |
Current CPC
Class: |
H01M 50/107 20210101;
H01M 50/538 20210101; H01M 50/103 20210101; Y02P 70/50 20151101;
Y02E 60/10 20130101 |
Class at
Publication: |
320/107 |
International
Class: |
H02J 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2002 |
JP |
2002-271943 |
Claims
What is claimed is:
1. A prismatic battery comprising: a battery case having a
substantially rectangular or elliptic cross section; a wound
electrode assembly of a positive electrode, a negative electrode,
and a separator interposed therebetween encased in said battery
case together with electrolyte, the electrodes comprising metal
substrates and respective active material layers applied thereon,
and projecting respectively on opposite ends of the assembly by
belt-shaped current collecting portions formed of bared edge
portions of the metal substrates of the electrodes, the portions
being not coated with the active material layers; and a positive
current collector and a negative current collector respectively
welded to end faces of the belt-shaped current collecting portions
of the electrodes, said current collectors each comprising: a metal
plate having a substantially rectangular or elliptic shape
conforming to a cross section of said electrode assembly; a pair of
lengthwise notches extending from central locations to outer edges
of lengthwise ends of the metal plate; a pair of widthwise notches
extending from central locations to outer edges of widthwise ends
of the metal plate; and connection pieces formed of opposing edges
of said lengthwise notches and said widthwise notches and
protruding orthogonally to the plane of the metal plate, wherein
weld joints are formed at intersections between said connection
pieces and said belt-shaped current collecting portions of the
electrodes.
2. The prismatic battery according to claim 1, wherein said
lengthwise notches are formed in a V shape and opened at a preset
angle, and said widthwise notches are formed in a square shape.
3. The prismatic battery according to claim 2, wherein said
lengthwise notches are opened at an angle ranging from 30.degree.
to 45.degree..
Description
[0001] The present disclosure relates to subject matter contained
in priority Japanese Patent Application No. 2002-271943, filed on
Sep. 18, 2002, the contents of which is herein expressly
incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a prismatic battery capable
of charging and discharging with a large current.
[0004] 2. Description of Related Art
[0005] With the progress of various portable electrical equipment,
the development of battery technologies is now given much weight.
Small rechargeable batteries using nickel metal hydride or lithium
have been developed for cycling applications such as mobile phones
and notebook PCs, and they are now beginning to find widespread
application in other high-power electrical equipment such as
electric tools, lawn mowers, and electric/gasoline hybrid cars.
Improved batteries having excellent large-current charge/discharge
characteristics are much desired for the application in high-power
equipment.
[0006] One means of achieving large-current charge/discharge
characteristics is to provide the battery with tabless current
collectors that have good high-rate charge/discharge
characteristics, as taught in Japanese Patent Laid-Open Publication
No. 2002-151047. Flat plate current collectors are directly welded
to the end faces of conductive portions, or bared edge portions
(belt-shaped current collecting portions) of metal substrates
without active materials thereon, of wound electrodes, so that
current is collected evenly from the entire electrodes.
[0007] FIG. 6 shows one example of such tabless current collectors,
denoted at 50. This current collector 50 is applied to cylindrical
batteries wherein wound electrode assemblies are encased in a
cylindrical case. Four rectangular notches 51 arranged with a
spacing of 90.degree. extend from near the center to the periphery
of a circular metal plate. Each two opposing sides of the
rectangular notches 51 are bent downward to form rib-like
protrusions 52.
[0008] The current collectors 50 are abutted on the end faces of
the opposite polarity belt-shaped current collecting portions
protruding from both ends of the wound electrode assemblies such
that the protrusions 52 are vertical. With the protrusions 52
extending across the belt-shaped current collecting portions of the
electrodes, they are welded thereto using a pair of weld electrodes
abutted to two longer side edges of the notches 51.
[0009] Prismatic batteries having a substantially rectangular or
elliptic cross section are more suitable for enabling thinner
designs of equipment than cylindrical batteries. Because of their
high space efficiency and excellent heat dissipation properties,
they are also considered a good candidate as a cell component of
battery pack or module used as the power source of high-power
electrical equipment.
[0010] Conventional prismatic batteries, however, do not employ the
above tabless current collectors. Most commonly, strip-like lead
plates or tabs, as they are called, of opposite polarity extend
from one end face of wound electrode assemblies, one of which is
directly welded to a sealing plate, while the other is welded to a
terminal plate that is electrically insulated from the sealing
plate. (see Japanese Patent Laid-Open Publication No. Hei.
11-25952, for example). Existing prismatic batteries in their
present form are therefore not suited as the power source of
high-power electrical equipment which requires charging and
discharging with a large current, simply because of the lack of
tabless current collectors designed for prismatic batteries.
[0011] U.S. Pat. No. 3,732,124 teaches another tabless current
collector for a cylindrical battery. As shown in FIG. 7, this
current collector 53 is made of a substantially square metal plate
having rib-like projections 54 formed by bending both lengthwise
edges downward at right angles, two U-shaped notches 57, and a hole
58 in the center for injecting electrolyte. Theoretically, this
current collector 53 could be modified to have a longer rectangular
shape conforming to the cross-sectional shape of prismatic
batteries and adopted as their tabless current collectors.
[0012] However, with the above current collectors 53 conformed to a
prismatic battery case, uniform electrical conduction across the
electrodes and current collectors 53 will not be achieved because
the pair of parallel projections 54 extending in the lengthwise
direction will be abutted only on the outer peripheral parts of the
belt-shaped current collecting portions of the electrodes. Also,
the welding will be difficult because the projections 54 are
arranged parallel to the belt-shaped current collecting
portions.
[0013] If the welding is performed with a pair of weld electrodes
abutted on both sides of the notch 57, a large idle current will
flow across the weld electrodes through the flat plate part of the
current collector 53 because of the relationship between the
electrical resistance and the length of the current path, as a
result of which the current flowing through the contact points
between the projections 54 and belt-shaped current collecting
portions will be too small to melt the contact points sufficiently
and to form firm weld joints. The contact resistance at the weld
joints will be accordingly large, and if the battery is discharged
at the rate of 3C (3 times the battery's capacity), for example,
the drop in voltage at the weld joints becomes large, leading to
reduced battery performance.
SUMMARY OF THE INVENTION
[0014] In light of the problems encountered in the prior art, it is
an object of the present invention to provide a prismatic battery
having tabless current collectors and being capable of charging and
discharging with a large current.
[0015] To achieve the above object, the present invention provides
a prismatic battery including: a case having a substantially
rectangular or elliptic cross section; a wound electrode assembly
of a positive electrode, a negative electrode, and a separator
interposed therebetween encased in the case together with
electrolyte, the electrodes comprising metal substrates and
respective active material layers applied thereon, and projecting
respectively on opposite ends of the assembly by belt-shaped
current collecting portions formed of bared edge portions of the
metal substrates of the electrodes, the portions being not coated
with the active material layers; and a positive current collector
and a negative current collector respectively welded to end faces
of the belt-shaped current collecting portions of the electrodes.
The current collectors each includes: a metal plate having a
substantially rectangular or elliptic shape conforming to the cross
section of the assembly; a pair of lengthwise notches extending
from central locations to outer edges of lengthwise ends of the
metal plate; a pair of widthwise notches extending from central
locations to outer edges of widthwise ends of the metal plate; and
connection pieces formed of opposing edges of the lengthwise
notches and widthwise notches and protruding orthogonally to the
plane of the metal plate, wherein weld joints are formed at
intersections between the connection pieces and the belt-shaped
current collecting portions of the electrodes.
[0016] The current collector of this prismatic battery has eight
connection pieces at opposing edges of the four notches, which are
formed radially from the central locations to the periphery, so
that the weld joints between the connection pieces and belt-shaped
current collecting portions of the electrodes are arranged evenly
over the entire end face of the belt-shaped current collecting
portions. Thereby, the battery is capable of high-rate charge and
discharge due to the enhanced current collection efficiency. The
notches decrease the idle current across the pair of weld
electrodes to a considerable extent because most of the weld
current flows through the shorter path and concentrates in the
intersections between the connection pieces and belt-shaped current
collecting portions rather than the detoured path through the metal
plate. Firm weld joints are thus formed, with the connection pieces
deeply biting into the belt-shaped current collecting portions. As
a result, the battery is capable of charging and discharging with a
large current due to the reduced internal resistance. Further, the
wide-open lengthwise notches allow easy pouring of electrolyte into
the case.
[0017] The prismatic battery of the invention is therefore capable
of high-rate charge and discharge, and of charging and discharging
with a large current, while satisfying the characteristics of
prismatic batteries such as high space efficiency and excellent
heat dissipation properties. This battery is particularly suited to
construct a battery pack or module for the power source of
high-power electrical equipment.
[0018] The battery case may have either a substantially rectangular
or elliptic, i.e., stretched circle, cross section.
[0019] Preferably, the lengthwise notches should be formed in a V
shape and opened at a preset angle, and the widthwise notches
should be formed in a square shape.
[0020] By forming the lengthwise notches in a V shape, the
connection pieces at the opposing edges of the notches intersect
with the belt-shaped current collecting portions of the wound
electrodes over the entire length. The weld joints, which are
formed at these intersections, are therefore located evenly from
the center to the periphery of the end face of the wound
electrodes, ensuring an increase in the current collection
efficiency.
[0021] The V-shaped lengthwise notches should preferably be opened
at an angle ranging from 30.degree. to 45.degree.. The angle should
be equal to or more than 30.degree. so as to ensure easy pouring of
electrolyte, but it should not exceed 45.degree., so that the weld
joints between the lengthwise connection pieces and belt-shaped
current collecting portions are arranged evenly along the length
over the end face of the wound electrodes, for achieving current
collection from the entire electrodes.
[0022] While novel features of the invention are set forth in the
preceding, the invention, both as to organization and content, can
be further understood and appreciated, along with other objects and
features thereof, from the following detailed description and
examples when taken in conjunction with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1A is a plan view of a prismatic battery according to a
first embodiment of the invention, and FIG. 1B is a schematic view
showing half of a longitudinal cross section of the battery;
[0024] FIG. 2 is a bottom view of a wound electrode assembly of the
prismatic battery, to which a current collector has been
welded;
[0025] FIG. 3 is a perspective view of the current collector;
[0026] FIG. 4 is a bottom view of an electrode assembly with a
current collector welded thereto of a prismatic battery according
to a second embodiment of the invention;
[0027] FIG. 5 is a bottom view of an electrode assembly with a
current collector welded thereto of a prismatic battery according
to a third embodiment of the invention;
[0028] FIG. 6 is a perspective view of a tabless current collector
used in a conventional cylindrical battery; and
[0029] FIG. 7 is a perspective view of another tabless current
collector used in a conventional cylindrical battery.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Preferred embodiments of the present invention will be
hereinafter described with reference to the accompanying
drawings.
[0031] FIG. 1A is a plan view of a prismatic battery according to a
first embodiment of the invention, and FIG. 1B is a schematic view
showing half of a longitudinal cross section of the battery. As is
seen from FIG. 1A, the prismatic battery includes a bottomed,
square tube case 1 having a substantially rectangular cross
section, in which are accommodated a wound electrode assembly 2
including a positive electrode 3 and a negative electrode 4, and a
separator 7 interposed therebetween, together with electrolyte (not
shown). A sealing plate 9 forming a sealing member 8 is fitted to
the open end of the battery case 1 and joined to the inner
peripheral edge of the case 1 by laser welding so as to seal the
case 1 in an air tight manner. The wound electrode assembly 2 will
be described in more detail later.
[0032] The sealing plate 9, which is substantially rectangular, has
a recess 10 at the center, in the middle of which a through hole 11
is formed. In the hole 11 is fitted an upper insulating gasket 12
made of electrolyte-resistant and electrically insulating synthetic
resin and coated with a sealant containing blown asphalt, upon
which a positive terminal 13 is attached. The positive terminal 13
is a rivet of nickel or nickel-plated steel, which is fixed to the
sealing plate 9 by swaging, with a lower insulating gasket 14 and a
washer or terminal plate 17 sandwiched between itself and the plate
9 such as to make tight contact with both gaskets 12, 14 to form an
air- and liquid-proof seal.
[0033] On one side of the positive terminal 13 (left side in FIG.
1A) in the sealing plate 9 is formed a discharge hole 19, which is
closed by a piece of nickel foil 20 fixedly attached to the inner
face of the plate 9, to form a safety vent 18 for preventing
explosion. On the opposite side of the positive terminal 13 (right
side) is another hole 12 for injecting a preset amount of
electrolyte after the sealing plate 9 is welded to the battery case
1. The hole 21 is closed by a plug 22 thereafter.
[0034] The positive electrode 3 has a metal substrate 23 of, e.g.,
metal foil, and active material layers 24 formed on both sides
thereof. The positive electrode 3 has a bared edge portion on one
side in the widthwise direction (upper side in FIG. 1B) where the
metal substrate 23 is not coated with the active material mixture.
This bared edge portion protrudes farther than the separator 7 in
the widthwise direction and functions as a belt-shaped current
collecting portion 27 of the positive electrode.
[0035] The negative electrode 4 has a metal substrate 28 of, e.g.,
thin punched metal sheet, and active material layers 29 formed on
both sides thereof. The negative electrode 4 has a bared edge
portion on one side in the widthwise direction (lower side in FIG.
1B), which protrudes farther than the separator 7 in the opposite
direction from the belt-shaped current collecting portion 27 of the
positive electrode, and functions as a belt-shaped current
collecting portion 30 of the negative electrode.
[0036] This embodiment shows one example of an alkaline
rechargeable battery; the active material layer 24 of the positive
electrode mainly contains nickel hydroxide, and the active material
layer 29 of the negative electrode mainly contains a
hydrogen-absorption alloy. The separator 7 is made of a
polypropylene or polyethylene nonwoven cloth that has undergone
hydrophilic treatment such as sulfonation. The electrolyte is a
solution of potassium hydroxide.
[0037] A positive electrode current collector 31 and a negative
electrode current collector 32 are welded to the end faces of the
belt-shaped current collecting portions 27 and 30 of the positive
and negative electrodes by resistance welding, respectively. The
battery has the wound electrode assembly 2 accommodated in the
prismatic case 1, and yet because of the novel structure, the
current is collected evenly from the entire positive and negative
electrodes 3, 4 by means of tabless current collectors. The
positive electrode current collector 31 is connected to the
terminal plate 17 with a lead plate 33, and the negative electrode
current collector 32 is connected to the bottom of the case 1 by
resistance welding.
[0038] While this embodiment shows one example in which the battery
case 1 has a substantially rectangular cross section, the invention
can also be applied to a case that has other cross-sectional shapes
such as an ellipse or stretched circle including parallel
lines.
[0039] FIG. 2 is a bottom view of the wound electrode assembly 2
with the current collectors 31, 32 welded thereto, and FIG. 3 is a
perspective view of the positive electrode current collector 31.
While the negative electrode current collector 32 has the size that
generally equals to that of the end face of the electrode assembly
2, the positive electrode current collector 31 is shaped somewhat
smaller than that, as seen from FIG. 1B. This is to prevent
short-circuiting caused by the collector 31 contacting the inner
face of the battery case 1, which is of opposite polarity.
[0040] The current collectors 31, 32 are metal plates 34 having an
elliptic shape conforming to the cross-sectional shape of the wound
electrode assembly 2. The metal plates 34 have deep V-shaped
notches 37 at both lengthwise ends, and narrow square notches 38 at
both widthwise ends (at the center along the longitudinal
direction) in a symmetrical arrangement.
[0041] The lengthwise notches 37 extend from two locations on both
sides of the center of the metal plate 34 toward lengthwise
direction, gradually spreading in the widthwise direction, to the
periphery of the metal plate 34. The narrow square widthwise
notches 38 extend from two locations on both sides in the widthwise
direction of the center to the periphery of the metal plate 34. The
opposing edges of the lengthwise notches 37 and widthwise notches
38 are bent downward to form rib-like connection pieces 39, 40, as
shown in FIG. 3.
[0042] These connection pieces 39, 40 of the current collectors 31,
32 are joined to the belt-shaped current collecting portions 27, 30
by resistance welding, using a pair of weld electrodes abutted on
the opposing edges of the notches 37, 38, with pressure and a
preset AC current being applied across the electrodes. The weld
electrodes should preferably have square tips that are long enough
to stretch over the edges of the notches 37, 38, so as to achieve
simultaneous welding of multiple intersections between the
connection pieces 39, 40 and belt-shaped current collecting
portions 27, 30.
[0043] The eight connection pieces 39, 40 formed at the opposing
edges of the four notches 37, 38 of the current collector 31, 32
are arranged radially from the center to the periphery of the
elliptic shape so that each connection piece 39, 40 extends
entirely across the belt-shaped current collecting portions 27, 30,
whereby the weld points between the connection pieces 39, 40 and
belt-shaped current collecting portions 27, 30 are evenly
distributed over the end face of the wound electrode assembly 2.
This structure enhances the current collection efficiency and
enables high-rate charge and discharge.
[0044] Because the connection pieces 39, 40 are bent orthogonally
to the metal plate 34, most of the current flows through the
intersections between the connection pieces 39, 40 and belt-shaped
current collecting portions 27, 30, which is the shorter path, and
there is very little idle current flowing across the pair of weld
electrodes, through the longer, detoured path along the periphery
of the notches 37, 38 in the metal plate 34. The weld current is
thus concentrated in small area, whereby the connection pieces 39,
40 firmly bite into the belt-shaped current collecting portions 27,
30, forming strong joints. The weld joints between the current
collectors 31, 32 and the belt-shaped current collecting portions
27, 30 thus have sufficient weld strength and tension strength,
whereby the internal resistance of the battery is reduced and
charging and discharging with a large current are made
possible.
[0045] When injecting electrolyte from the hole 21 after encasing
the electrode assembly 2 with the current collectors 31, 32 into
the battery case 1, the lengthwise notches 37 are useful as a
guide, enabling smooth pouring of the electrolyte. For this
purpose, the lengthwise notches 37 should preferably be opened at
an angle of equal to or more than 30.degree.. This angle may be
determined in accordance with the length and width of the current
collectors 31, 32, but it should not exceed 45.degree.. If the
angle is over 45.degree., then the weld joints between the
connection pieces 39 and belt-shaped current collecting portions
27, 30 will be located too much toward the center of the electrode
assembly 2, and current collection from the lengthwise ends of the
electrode assembly 2 will be insufficient.
[0046] The prismatic battery of the invention employs a prismatic
battery case 1 and therefore can advantageously be used in thin
equipment. It has high space efficiency and excellent heat
dissipation properties, and is capable of high-rate charge and
discharge, and of charging and discharging with a large current.
This battery is therefore particularly suitable for constructing a
battery pack or module to form a power source of high-power
electrical equipment.
[0047] FIG. 4 is a bottom view of an electrode assembly 2 of a
prismatic battery according to a second embodiment of the
invention, to which a current collector 41 has been welded.
Elements that are identical or similar to those of FIG. 2 are given
the same reference numerals. The current collector 41 differs from
that of FIG. 2 in that lengthwise notches 42 are formed in a
truncated V shape, and that the notches 42 open at a wider angle
than that of the current collector 32. This current collector
allows even easier pouring of electrolyte, while achieving the same
effects as with the first embodiment.
[0048] FIG. 5 is a bottom view of an electrode assembly 2 of a
prismatic battery according to a third embodiment of the invention,
to which a current collector 43 has been welded. Elements that are
identical or similar to those of FIG. 2 are given the same
reference numerals. The current collector 43 differs from the
current collector 32 in that lengthwise notches 44 are formed in a
rectangular shape, and widthwise notches 47 are made shorter to
form a circular hole 48 therebetween for injecting electrolyte. As
compared to the foregoing embodiments, this prismatic battery
allows pouring of electrolyte with less ease, and the connection
pieces 39 and belt-shaped current collecting portions 27, 30
intersect each other in a slightly shorter distance. Nevertheless,
it is clearly different from the conventional battery with the
current collector 53 of FIG. 7, and is capable of high-rate charge
and discharge, and of charging and discharging with a large
current.
[0049] As described above, the current collectors of the prismatic
battery of the invention have radially arranged connection pieces
that are engaged with and welded to the belt-shaped current
collecting portions of the electrode assembly. The battery is
therefore capable of high-rate charge and discharge due to the
enhanced current collection efficiency. The idle current during
welding is made low by the notches in the current collectors,
whereby the weld current concentrates in the intersections between
the connection pieces and belt-shaped current collecting portions.
The resultant firm weld joints ensure a low internal resistance and
enable the battery to charge and discharge with a large current.
The notches formed in the lengthwise direction are also useful when
pouring liquid electrolyte into the battery. The prismatic battery
thus satisfies all the characteristics of prismatic batteries that
are suitable for thin equipment, and have high space efficiency and
excellent heat dissipation properties, and is capable of high-rate
charge and discharge, and of charging and discharging with a large
current.
[0050] Although the present invention has been fully described in
connection with the preferred embodiment thereof, it is to be noted
that various changes and modifications apparent to those skilled in
the art are to be understood as included within the scope of the
present invention as defined by the appended claims unless they
depart therefrom.
* * * * *